I am generating a number of csv files dynamically, using the following code:
import csv
fieldnames = ['foo1', 'foo2', 'foo3', 'foo4']
with open(csvfilepath, 'wb') as csvfile:
csvwrite = csv.DictWriter(csvfile, delimiter=',', fieldnames=fieldnames)
csvwrite.writeheader()
for row in data:
csvwrite.writerow(row)
To save space, I want to compress them.
Using the gzip module is quite easy:
with gzip.open("foo.gz", "w") as csvfile :
csvwrite = csv.DictWriter(csvfile, delimiter=',', fieldnames=fieldnames)
csvwrite.writeheader()
for row in data:
csvwrite.writerow(row)
But I want the file in 'zip' format.
I tried the zipfile module, but I am unable to directly write files into the zip archive.
Instead, I have to write the csv file to disk, compress them in a zip file using following code, and then delete the csv file.
with ZipFile(zipfilepath, 'w') as zipfile:
zipfile.write(csvfilepath, csvfilename, ZIP_DEFLATED)
How can I write a csv file directly to a compressed zip similar to gzip?
Use the cStringIO.StringIO object to imitate a file:
with ZipFile(your_zip_file, 'w', ZIP_DEFLATED) as zip_file:
string_buffer = StringIO()
writer = csv.writer(string_buffer)
# Write data using the writer object.
zip_file.writestr(filename + '.csv', string_buffer.getvalue())
Thanks kroolik
It's done with little modification.
with ZipFile(your_zip_file, 'w', ZIP_DEFLATED) as zip_file:
string_buffer = StringIO()
csvwriter = csv.DictWriter(string_buffer, delimiter=',', fieldnames=fieldnames)
csvwrite.writeheader()
for row in cdrdata:
csvwrite.writerow(row)
zip_file.writestr(filename + '.csv', string_buffer.getvalue())
Having IOString to store every bytes in memory could be very memory consuming.
Based on the zipfile module documentation after creating a ZipFile object, all individual files has to be opened. Like this:
with ZipFile('spam.zip') as myzip:
with myzip.open('eggs.txt') as myfile:
print(myfile.read())
This example can be used for write as well...
Related
I'm trying to read sentences in a csv file, convert them to lowercase and save in other csv file.
import csv
import pprint
with open('dataset_elec_4000.csv') as f:
with open('output.csv', 'w') as ff:
data = f.read()
data = data.lower
writer = csv.writer(ff)
writer.writerow(data)
but I got error "_csv.Error: sequence expected". What should I do?
*I'm a beginner. Please be nice to me:)
You need to read over your input CSV row-by-row, and for each row, transform it, then write it out:
import csv
with open('output.csv', 'w', newline='') as f_out:
writer = csv.writer(f_out)
with open('dataset_elec_4000.csv', newline='') as f_in:
reader = csv.reader(f_in)
# comment these two lines if no input header
header = next(reader)
writer.writerow(header)
for row in reader:
# row is sequence/list of cells, so...
# select the cell with your sentence, I'm presuming it's the first cell (row[0])
data = row[0]
data = data.lower()
# need to put data back into a "row"
out_row = [data]
writer.writerow(out_row)
Python contains a module called csv for the handling of CSV files. The reader class from the module is used for reading data from a CSV file. At first, the CSV file is opened using the open() method in ‘r’ mode(specifies read mode while opening a file) which returns the file object then it is read by using the reader() method of CSV module that returns the reader object that iterates throughout the lines in the specified CSV document.
import csv
# opening the CSV file
with open('Giants.csv', mode ='r')as file:
# reading the CSV file
csvFile = csv.reader(file)
# displaying the contents of the CSV file
for lines in csvFile:
print(lines)
I have a csv file and I want to transfer the raw data without the headers to a new csv file and have the rows and columns the same as the original.
IRIS_data = "IRIS_data.csv"
with open(IRIS_data, 'wb') as data:
wr = csv.writer(data, quoting=csv.QUOTE_ALL)
with open(IRIS) as f:
next(f)
for line in f:
wr.writerow(line)
The code above is my most recent attempt, when I try run it I get the following error:
a bytes-like object is required, not 'str'
It's because you opened the input file with with open(IRIS_data, 'wb'), which opens it in binary mode, and the output file with just with open(IRIS) which opens it in text mode.
In Python 3, you should open both files in text mode and specify newline='' option)—see the examples in the csv module's documentation)
To fix it, change them as follows:
with open(IRIS_data, 'w', newline='') as data:
and
with open(IRIS, newline='') as f:
However there are other issues with you code. Here's how to use those statements to get what I think you want:
import csv
IRIS = "IRIS.csv"
IRIS_data = "IRIS_data.csv"
with open(IRIS, 'r', newline='') as f, open(IRIS_data, 'w', newline='') as data:
next(f) # Skip over header in input file.
writer = csv.writer(data, quoting=csv.QUOTE_ALL)
writer.writerows(line.split() for line in f)
Contents of IRIS_data.csv file after running the script with your sample input data:
"6.4","2.8","5.6","2.2","2"
"5","2.3","3.3","1","1"
"4.9","2.5","4.5","1.7","2"
"4.9","3.1","1.5","0.1","0"
"5.7","3.8","1.7","0.3","0"
"4.4","3.2","1.3","0.2","0"
"5.4","3.4","1.5","0.4","0"
"6.9","3.1","5.1","2.3","2"
"6.7","3.1","4.4","1.4","1"
"5.1","3.7","1.5","0.4","0"
You have to encode the line you are writing like this:
wr.writerow( line.encode(”utf8”))
Also open your file using open(..., ‘wb’). This will open the file in binary mode. So you are certain the file is actually open in binary mode. Indeed it is better to now explicitly the encoding than assuming it. Enforcing encoding for both reading and writing will save you lots of trouble.
I have a script that successfully removes a column from a csv file. Currently it does this by creating a new file. I want it to write to the original file rather than create a new one.
I’ve tried this by using the r+ mode for open but it’s not working how I want. See notes below. I think r+ mode is the one I need but I’m struggling to find working examples to learn from.
my code:
import csv
in_file = "Path to Source"
out_file = "Path to Result"
with open(in_file, 'r', newline='') as inf, \
open(out_file, 'w', newline='') as outf:
reader = csv.reader(inf)
writer = csv.writer(outf)
for r in reader:
writer.writerow((r[0],r[1],r[2],r[3],r[4],r[5],r[6]))
attempt using r+ mode:
with open(in_file, 'r+', newline='') as inf:
reader = csv.reader(inf)
writer = csv.writer(inf)
for r in reader:
writer.writerow((r[0],r[1],r[2],r[3],r[4],r[5],r[6]))
This fails with the error list index out of range
From what I see, as the reader reads, the writer writes. On the same file.
Files have a 'cursor', i.e. a current position upon which they are read from/written to.
So the writer is overwriting the next row in the file after the one the reader has just read, with catastrophic consequences on the following readings.
I think the first approach is the best one: create a new file and then rename it (the original input file is deleted automatically)
import csv, os
in_file = "Path to Source"
out_file = "Path to Result"
with open(in_file, 'r', newline='') as inf, \
open(out_file, 'w', newline='') as outf:
reader = csv.reader(inf)
writer = csv.writer(outf)
for r in reader:
writer.writerow(r[:7])
os.rename(out_file, in_file)
I am trying to write to a .tsv file using python's CSV module, this is my code so far
file_name = "test.tsv"
TEMPLATE = "template.tsv"
fil = open(file_name, "w")
# Added suggested change
template = csv.DictReader(open(TEMPLATE, 'r'), delimiter='\t')
new_file = csv.DictWriter(fil, fieldnames=template.fieldnames, delimiter='\t')
new_file.writeheader()
basically TEMPLATE is a file that will contain the headers for the file, so i read the headers using DictReader and pass the fieldnames to DictWriter, as far as i know the code is fine, the file test.tsv is being created but for some reason the headers are not being written.
Any help as to why this is happening is appreciated, thanks.
DictReader's first argument should be a file object (create with open()), cf. http://docs.python.org/py3k/library/csv.html#csv.DictReader
You forgot open() for the TEMPLATE file.
import csv
file_name = "test.tsv"
TEMPLATE = "template.tsv"
fil = open(file_name, "w")
# you forgot this line, which will open the file
template_file = open(TEMPLATE, 'r')
template = csv.DictReader(template_file, delimiter='\t')
new_file = csv.DictWriter(fil, fieldnames=template.fieldnames, delimiter='\t')
new_file.writeheader()
Try to give DictReader opened file instead of file name:
csv.DictReader(open(TEMPLATE, 'r'), delimiter='\t')
Same for the writer, but opened for writing.
I am trying to read and write on the same CSV file:
file1 = open(file.csv, 'rb')
file2 = open(file.csv, 'wb')
reader = csv.reader(file1)
writer = csv.writer(file2)
for row in reader:
if row[2] == 'Test':
writer.writerow( row[0], row[1], 'Somevalue')
My csv files are:
val1,2323,Notest
val2, 2323,Test
So basically if my row[2] value is Test I want to replace it with Some new value.
The above code gives me empty CSV files.
You should use different output file name. Even if you want the name to be the same, you should use some temporary name and finally rename file.
When you open file in 'w' (or 'wb') mode this file is "cleared" -- whole file content disappears. Python documentation for open() says:
... 'w' for only writing (an existing file with the same name will be erased), ...
So your file is erased before csv functions start parsing it.
You can't open a file in both read and write modes at once.
Your code could be modified as follows:-
# Do the reading
file1 = open(file.csv, 'rb')
reader = csv.reader(file1)
new_rows_list = []
for row in reader:
if row[2] == 'Test':
new_row = [row[0], row[1], 'Somevalue']
new_rows_list.append(new_row)
file1.close() # <---IMPORTANT
# Do the writing
file2 = open(file.csv, 'wb')
writer = csv.writer(file2)
writer.writerows(new_rows_list)
file2.close()
As Jason points out, if your CSV is too big for your memory, then you'll need to write to a different filename and then rename it. This will likely be a bit slower.
If your csv file is not big enough(to explode the memory), read it all into memory and close the file before open it in write mode.
Or you should consider writing to a new file rather than the same one.
It is not possible to open the same file in two different modes in python.You have to release one of the file pointers with file_name.close() before opening the file in another mode!